Tropical Storm Isaac battered impoverished Haiti Saturday, leaving at least two people dead, as southern Florida braced for a possible hurricane during the Republican convention.

With winds of up to 95 kilometers (60 miles) per hour, the storm was expected to sweep across Cuba at night and become a hurricane on Sunday as it nears Florida, according to the US National Hurricane Center.

A hurricane warning was in effect for the Florida Keys and parts of the state's southwest coast, the Miami-based NHC said, raising concerns the storm could disrupt the Republican National Convention opening in Tampa on Monday.

The forecasters said Isaac was near hurricane strength when the eye of the storm passed over Haiti, where hundreds of thousands of people are still living in squalid, makeshift camps following a catastrophic 2010 earthquake.

An eight-year-old Haitian girl died when a wall collapsed at her home and a 51-year-old woman died when her roof collapsed, according to officials. They were the first two known casualties of the storm.

Haiti was the poorest country in the Western Hemisphere even before the earthquake killed 250,000 people, and some 400,000 are still living in tent camps in and around the devastated capital Port-au-Prince.

More than 3,300 families had been evacuated to temporary shelters ahead of the storm as aid groups provided clean water and hygiene kits to try to limit the risk of contaminated water and the spread of disease.

Isaac was 65 kilometers north of Cuba as it swirled along the coast to the northwest at 28 kilometers per hour, the NHC said in its latest bulletin, issued at 2:00 pm (1800 GMT).

Cuba declared a state of alert in the island's six eastern provinces, where nearly five million people live, and evacuated some 5,000 foreign and local tourists from beachside hotels.

Local authorities "must understand the possible impact of the intense rain on dams, canals and rivers," the Cuban civil defense office said, warning of blocked water drainage systems and flooded roads.

But officials noted that eastern reservoirs are at very low levels, helping mitigate the risk of flooding.

After striking Haiti and southeastern Cuba, home to the US naval base and "war on terror" prison at Guantanamo Bay, Isaac was on course for a hit at or near the Florida Keys off the southern tip of the United States.

Isaac could reach mainland Florida early Monday, coinciding with the Republican convention, when tens of thousands of people will descend on Tampa for speeches, parties and the formal nomination of former Massachusetts governor Mitt Romney to take on President Barack Obama in November 6 elections.

Florida Governor Rick Scott declared a state of emergency on Saturday but insisted it was a "normal step" ahead of any storm and that the convention in Tampa would go ahead as planned.

"We are going to have a great convention," he told reporters.

Tampa Mayor Bob Buckhorn also sought to calm jitters about the weather, saying the storm might bring heavy rain to Tampa on the first of the four-day convention but would be followed by sunny skies.

"There will be rain and wind on Monday, but the remaining three days of the convention ought to be beautiful. We are prepared for it and we train for this," Buckhorn told Fox News.

"There may be wet shoes, but every day after Monday ought to be fine."

Vice President Joe Biden has canceled a trip to Tampa because of the approaching storm, Obama's Democratic campaign said.

In the Gulf of Mexico, BP evacuated its Thunder Horse platform, the world's largest offshore production and drilling facility.